Genentech said Wednesday that its drug for Alzheimer's disease produced mixed results in two midstage clinical trials, raising questions as to whether parent company Roche will now pay to test the therapy in larger, more expensive trials.

Pharmaceutical companies like Roche are trying to develop therapies for the brain-destroying disease that affects an estimated 35 million people worldwide.

Genentech's drug, crenezumab, was tested in two phase II trials. In the first trial, 431 patients with mild to moderate Alzheimer's received a high dose, a low dose or a placebo over 73 weeks. Although the overall group did not experience a statistically significant reduction in cognitive decline compared with the placebo, the patients with the mildest disease demonstrated a 35.4 percent reduction in cognitive decline and a nearly 20 percent reduction in global functional decline, or the ability to perform everyday activities.

The smaller study, with 91 patients, showed similar results: a 52 percent reduction in cognitive decline and a 41.5 percent reduction in functional decline.

Crenezumab is a monoclonal antibody that clears buildups of amyloid beta from the brain, getting rid of a protein believed by many scientists to play a role in the development of Alzheimer's. But other, similar drugs, such as those by Eli Lilly and the team of Johnson & Johnson and Pfizer, have failed in late-stage trials before.

Genentech licensed crenezumab from AC Immune, a Swiss biopharmaceutical company whose executives suggested that the results were promising enough to continue testing the drug in trials.

"These very promising crenezumab data show this antibody is one of the best performing therapies tested so far in Phase II for Alzheimer's disease," said AC Immune CEO Andrea Pfeifer in a statement. "The unique combination of its safety profile and proven mechanism-of-action could potentially allow crenezumab to be given to patients at efficacious doses without the side effects that have hampered other therapies."